1. Field of the Invention
The present invention relates to a multi charged particle beam writing apparatus. More specifically, for example, the present invention relates to a method of correcting aberrations produced when irradiating multi-beams onto a target object on the stage.
2. Description of Related Art
The lithography technique that advances miniaturization of semiconductor devices is extremely important as a unique process whereby patterns are formed in semiconductor manufacturing. In recent years, with high integration of LSI, the line width (critical dimension) required for semiconductor device circuits is decreasing year by year. The electron beam (EB) writing technique, which intrinsically has excellent resolution, is used for writing or “drawing” a pattern on a wafer and the like with electron beams.
As an example employing the electron beam writing technique, a writing apparatus using multiple beams (multi beams) can be cited. Compared with the case of writing a pattern by using a single electron beam, since it is possible to emit multiple beams at a time in multi-beam writing, the throughput can be greatly increased. For example, in a writing apparatus employing a multi-beam system, multiple beams are formed by letting an electron beam emitted from an electron source assembly pass through a mask with a plurality of holes, blanking control is performed for each of the beams, and each unblocked beam irradiates a desired position on a target object (refer to, e.g., Japanese Published Unexamined Patent Application (JP-A) No. 2006-261342).
In multi beam writing, since the beam size of the entire multi-beams is large, aberrations on the optical axis of a crossover image forming system become large. Therefore, it is necessary to form an aperture (contrast aperture) for blanking arranged near a crossover to have a large aperture diameter. However, when the diameter of the aperture is large, a new problem occurs in that it becomes necessary to increase a blanking voltage for blanking control. Therefore, it is desirable to make geometric aberrations themselves of multi-beams small.